A charged particle beam device represented by an electron scanning microscope needs to maintain an optical system and a specimen chamber in a vacuum, and when an electron beam is irradiated, an electron optical system and the specimen chamber is evacuated. Furthermore, an atmosphere surrounding an electron source (charged particle source) emitting an electron beam needs to maintain an extremely high degree of vacuum. The technology of blocking an atmosphere on the specimen chamber side in which the degree of vacuum is lowered or could be lowered from an atmosphere on the electron source side when the specimen is replaced, is disclosed in Patent Literatures 1 to 3.